Osmoregulation and Excretion in Humans part 2

Question 1

Normal conditions

Answer 1

• 1,600 L of blood flows through a pair of human kidneys each day, yielding about 180 L of initial filtrate
• Both the volume and composition of the filtrate are changed dramatically as processing occurs
• About 99% of the water and nearly all of the sugars, amino acids, vitamins, and other organic nutrients are reabsorbed
• Leaves about 1.5 L of urine to be transported to bladder

Question 2

Osmosis direction

Answer 2

-Water diffuses from where ITS concentration is HIGH (dilute solute) to where ITS concentration is low (concentrated solute)

Question 3

Osmolarity (osmotic concentration)

Answer 3

• The measure of solute concentration
• The number of osmoles of solute per liter of solution
• In the kidneys, we’re looking at concentrations of Na+ and Cl- as solutes

Question 4

Goals of the kidneys

Answer 4

• Removing metabolic wastes/toxins

- Osmoregulation - salt and water balance

Question 5

Initial filtration

Answer 5

Occurs at the filtration membrane

non-specific

Filtration occurs at filtration slits

anything small enough to fit between slits enters the nephron (glucose, amino acids, vitamins, and toxins)

-Cells and large proteins are trapped in capillaries

Question 6

With normal kidney function, which is present in plasma but not in filtrate

Answer 6

Proteins and blood cells

Question 7

What is the descending limb permeable to

Answer 7

Only water

Question 8

What is the ascending limb permeable to

Answer 8

Only Na+ and Cl-

May leave nephron by passive or active transport

Question 9

What does the movement of salts out of the ascending limb create?

Answer 9

The solute gradients

Question 10

Proximal convoluted tubule (PCT)

Answer 10

-Closely associated with peritubular capillaries bed

Function:

• Passive and active transport (need energy for active)
• Reabsorption of water, ions, glucose, and amino acids into capillaries (co-transport with Na+)
• Secretion of nitrogenous wastes and toxins (ex. aspirin, morphine)

(Numbers in nephron indicate the osmolarity (amount of solute) in the filtrate)

Question 11

Nephron loop (Loop of Henle) 
Main function

Answer 11

• Major function is to use active transport to move Na+ and Cl- into the kidney medulla
• Associated with vasa recta capillary bed

Question 12

Nephron Loop (descending limb)

Answer 12

• Descending limb is only permeable to water
• Osmolarity of medulla increase moving away from cortex
• Water moves via osmosis through aquaporins and is reabsorbed into the blood concentrating the filtrate in nephron

Question 13

Nephron Loop (ascending limb)

Answer 13

• Ascending limb is only permeable to ions (primarily Na+ and Cl-)
• In thin segment NaCl, which had become concentrated in descending limb, diffuses out of nephron (helps maintain high osmotic concentration)
• In thick segment, NaCl is actively transported out and filtrate becomes more dilute

Question 14

Distal convoluted tubule (DCT)

Answer 14

• Reabsorption of water is influenced by hormones
• Secretion of any extra wastes
• Important site of proton (H+) absorption or secretion
• Works with respiratory system to balance pH

Question 15

Carbon Dioxide transport

Answer 15

• Dissolved in blood plasma (~10%)
• Bound to hemoglobin (~20%)
• In the form of plasma bicarbonate (~70%)
• In many respects, [CO2] more important in determining respiratory rate

Question 16

Homeostatic response

Answer 16

Include coordination between respiratory efferent pathways and urinary secretion/reabsorption of proteins

Question 17

What happens if there is a problem with the DCT that prevents the secretion/absorption of protons (H+)

Answer 17

It can lead to metabolic acidosis or metabolic alkalosis

Associated with bicarbonate excess or deficiency

Question 18

Metabolic acidosis

Answer 18

Too many protons

Question 19

Metabolic alkalosis

Answer 19

Too few protons

Question 20

What is the concentration of carbonic acid in the blood dependent on

Answer 20

The level of CO2 in the body and the amount of CO2 gas exhaled through the lungs

Question 21

Carbonic acid lost and formed regarding CO2

Answer 21

A molecule of carbonic acid is lost for every molecule of CO2 exhaled, and a molecule of carbonic acid is formed for every molecule of CO2 retained

(The respiratory contribution to acid-base balance is usually discussed in terms of CO2 rather than of carbonic acid)

Question 22

Respiratory acidosis

Answer 22

CO2 excess

Can result from anything that interferes with respiration, such as pneumonia, emphysema, or congestive heart failure

Question 23

Respiratory alkalosis

Answer 23

CO2 deficiency

Occurs when too much CO2 is exhaled from the lungs, as occurs in hyperventilation

Question 24

Hypercapnia

Answer 24

Too much carbon dioxide, increase in protons, decreases pH

Results in acidosis (acidic blood)

Question 25

Hypocapnia

Answer 25

Too little carbon dioxide, decrease in protons, raises pH

Results in alkalosis (basic blood)

Question 26

Water conservation in the collecting duct

Answer 26

Main function: absorb more water

Relies on the solute gradient that was created by the nephron loop (osmosis drive water to be reabsorbed from the duct)

Influenced by hormones

Question 27

Steps in the kidney

Answer 27

1: Initial filtration
2: Reabsorption/Secretion at the PCT
3: “Salty” medulla in the Nephron Loop
4: Reabsorption/Secretion at the DCT
5: Water conservation in the collecting duct